Pickle a django query? | 易学教程

问题

Is it possible to pickle or somehow store a django query in the database? This won`t work :

u = User.objects.all 
import cPickle
pickled_query = cPickle.dumps(u) # and store the pickled_query in a db-field.

Any thoughts?

Updated:

import cPickle

class CustomData(models.Model):
    name = models.CharField(max_length = 30)
    pickled_query = models.CharField(max_length = 300)

def get_custom_result(self):
    q = cPickle.loads(self.pickled_query)
    return q()

>>> cd = CustomData(name="My data", pickled_query=cPickle.dumps(User.objects.all))
>>> cd.save()
>>> for item in cd.get_custom_result(): print item
# prints all the users in the database, not printing the query result 
# when pickled, but when called like cd.get_custom_result(), that is when 
# the query is actually executed.

Now that's what I want to do. I know this actual piece of code won`t run, but it shows my intention; to store a query, not the result, and execute that query at some point in the future.

Update #2:

>>> from django.contrib.auth.models import User
# adds two users; super and test
>>> u = User.objects.filter(username = 'test')
>>> import cPickle
>>> s = cPickle.dumps(u.query)
>>> s2 = cPickle.loads(s)
>>> o = s2.model.objects.all()
>>> o.query = s2
>>> for i in o: print i
...
super

Still not completly satisfied. I know QuerySets are lazy so doing s2.model.objects.all() won't execute a query fetching all users?

回答1:

There's documentation for that. Basically, pickle the query attribute if you want to recreate the SQL query, and pickle the whole queryset if you want to pickle a snapshot of the current results.

Your example would do the latter, if you pickled the result of all() instead of the bound method.

来源：https://stackoverflow.com/questions/5715479/pickle-a-django-query

标签

python

django

pickle